In a conventional silent chain, link plates having pairs of pin holes are arranged alternately in guide rows and non-guide rows with the link plates of each row interleaved with link plates of a preceding row and a following row to provide a chain in the form of an endless loop. The rows of link plates are connected by pins that extend through the pin holes in the link plates. Guide plates are arranged at both ends of each guide row and the pins are press-fit into pin holes of the guide plates but fit loosely in the pin holes of the other plates of the chain to allow articulation of the guide rows relative to the non-guide rows. Each of the guide plates has an inner side facing toward the inside of the loop formed by the chain, and an outer side facing toward the outside of the loop. The outer side of each guide plate is typically substantially flat in a direction parallel to a pitch line which connects the centers of the pin holes of the guide plate. Such a chain is described in United States Patent Publication 2011/0224041, published on Sep. 15, 2011.
Another known silent chain, depicted in Japanese laid-open Patent Application No. H8-35541, includes guide links each having a base portion, a pair of openings spaced from each other, a pair of toe portions spaced from each other and extending upwardly, and a crotch portion connecting inner flank surfaces of the pair of toe portions.
FIGS. 12 and 13 show a guide plate 520 in a silent chain 500 of the kind described in United States Patent Publication 2011/0224041. This guide plate is placed under tension in the longitudinal direction of the guide plate. Elastic deformation of plate 520 in the longitudinal direction of the chain is more restricted than the lateral elastic deformation of the toothed link plates 510 of the chain because the guide plate 520 has a smaller cut-away portion than the cut-away portion of a link plate 510. Consequently, as shown in FIG. 13, the connecting pins 530 extending through a plurality of link plates 510 in a guide row and a pair of the guide plates 520 at the ends of the guide row become bent or bowed, and become out of parallel with pin holes 511 of the link plates 510. This departure from a parallel relationship between the pins 511 and the pin holes of the link plates results in uneven wear, referred to as “galling” on the surfaces of the connecting pins 510 where they are contacted by the link plates 510.
Because the connecting pins 530 become out of parallel with the pin holes 511 due to bending, the tensile load acting on the link plates 510 becomes unbalanced, and is concentrated on the outermost link plates 510. Consequently, the outermost link plates more easily undergo abrasive wear and or more subject to the formation of cracks, and the fatigue strength of the chain as a whole decreases.
As shown in FIG. 14, when the link plates 510 of a guide row GL engage a sprocket S, a space created between teeth 510t of the link plates of the guide row and a sprocket tooth St of the sprocket S becomes sealed by an adjacent pair of guide plates 520. Air confined in this space is compressed and generates an unpleasant explosive sound when released.
On the other hand, in a silent chain having a guide link of the kind described in Japanese laid-open Patent Application No. H8-3554, and shown in FIGS. 15 and 16, when a guide link 610 is placed under longitudinal direction, the toe portions 613, which extend toward the outside of the loop formed by the chain are pulled in opposite directions. The tensile force tends to form a crack at a crotch portion 614 of the guide plate. At the same time, side of the guide link 610 facing toward the inside of the loop is compressed in the longitudinal direction, and the guide link 610 warps, causing the pin holes to become out of parallel with connecting pins. Here again, uneven wear causes galling of the surfaces of the connecting pins where they contact the pin holes.
This invention addresses the above-described problems, and it is an object of the invention to achieve one or more of the following results: suppression of bending or bowing of connecting pins; reduction of wear elongation of the chain; increase in the fatigue strength of the chain; extension of the useful life of the chain; and reduction of noise due to the confinement of air between link teeth and sprocket teeth.